1. Field of the Invention
The present invention relates to a cooling circuit for a motor vehicle, and, more particularly, to a cooling circuit for a motor vehicle in which a hydrodynamic retarder is located.
2. Description of the Related Art
In addition to so-called oil retarders which are operated with oil as the working medium that is circulated in a proprietary working medium circuit of the retarder, so-called water retarders are known which are tied directly into the cooling circuit of a motor vehicle which, as a rule is operated with water or a water mixture as the cooling medium. Accordingly, the working medium of the retarder is at the same time the cooling medium of the cooling circuit.
Whereas in the case of the previously mentioned oil retarders an additional heat exchanger must be provided in order to remove the heat that is generated during braking operation of the hydrodynamic retarder from the working medium, for example into the cooling circuit of the motor vehicle, such a separate heat exchanger may be foregone in the case of the water retarders, since the heat of the hydrodynamic retarder is absorbed in the retarder immediately by the cooling medium and can therefore be removed via the heat exchanger of the cooling circuit (motor vehicle radiator) that is provided anyhow.
Examples of such hydrodynamic retarders that are tied into the cooling circuit of the motor vehicle and which relate to the current invention are disclosed in the following publications: EP 0 719 683 A2; DE 297 07 304 U1; DE 196 16 427 A1; EP 1 251 050 B1; DE 1 530 672 A; and EP 1 646 771 B1.
In practice it has been proven to be disadvantageous that—due to the direct integration of the hydrodynamic retarder into the cooling circuit of the motor vehicle—an increased flow resistance for the cooling medium may occur which has to be overcome by the cooling medium pump. In unfavorable circumstances therefore, utilization of a cooling medium pump having a comparatively greater output compared to cooling circuits without hydrodynamic retarders becomes necessary. According to EP 1 646 771 B1 various measures are suggested in order to avoid the necessity of a more powerful cooling medium pump which can lead to increased fuel consumption.
WO 97/33077 describes one design example with a hydrodynamic retarder in the cooling circuit of a motor vehicle wherein an especially minimal retarder braking torque can be adjusted through a short-circuit circuit that branches off downstream of the hydrodynamic retarder and ends upstream from the cooling medium pump.
Due to the increasing importance of an as low a power consumption as possible of the cooling medium pump the requirement to reduce the flow resistance in a cooling circuit for a motor vehicle with a directly tied-in hydrodynamic retarder exists in spite of the already suggested measures.
What is needed in the art is an improved cooling circuit for a motor vehicle.